1. Field of the Invention
The present invention relates to a single focus lens favorably used for a small-sized apparatus having an image pick-up feature, for example, a mobile telephone having a camera feature, a PDA (Personal Digital Assistant), and a digital still camera, etc.
2. Description of the Related Art
An image pick-up device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) is used in an image pick-up apparatus such as a digital still camera. In recent years, such an image pick-up device has been further remarkably downsized. Therefore, it has been demanded that a pick-up apparatus and a lens built in the pick-up apparatus are downsized and reduced in weight. Also, in recent years, an image pick-up device having a large number of pixels has been developed in order to achieve high image quality. In line therewith, performance by which high resolution and high contrast can be brought about is required for the lens system.
For example, a pick-up lens described in the following JP-A-10-48516 is available as an image pick-up lens used for such an image pick-up apparatus. JP-A-10-48516 describes an image pick-up lens composed of three lenses which are the first, the second and the third lenses in order from the object side. In the image pick-up lens, the power of the first lens is low, and an aperture stop is disposed between the second lens and the third lens.
In regard to recent image pick-up devices, downsizing and high concentration of pixels have been advanced as described above. In line therewith, high resolution performance and compacting in structure has been demanded for an image pick-up lens. The image pick-up lens described in JP-A-10-48516 described above has achieved performance and compactness to some degree with a fewer number of a lenses of three-lens construction. However, it is desired that a lens system of further compactness and higher performance is developed.